Not Medical Advice: A cyst is a fluid-containing sac. A lesion is a general word for the site of an injury or wound.
A cyst is a sac that may be filled with air, fluid or other material. A cyst can form in any part of the body, including bones, organs and soft tissues. Most cysts are noncancerous (benign). Although cancers can form cysts.
Some common examples of cysts include sebaceous (epidermoid) cysts — small bumps that form just beneath the skin — cysts that occur in the liver (hepatic), cysts that occur in the kidneys (renal), and breast and ovarian cysts. It's important to note, however, that nearly all cancers are capable of producing cysts.
A lesion can be almost any abnormal change involving any tissue or organ due to disease or injury. There are numerous types of lesions with different naming classifications.
Lesions can be categorized according to whether or not they are caused by cancer. A benign lesion is non-cancerous whereas a malignant lesion is cancerous. Lesions can be defined according to the patterns they form. For example, a bull's-eye or target lesion is one that looks like the bull's eye on a target.
Lesions can also be categorized by their size. A gross lesion is one that can be seen with the naked eye. A microscopic or histologic lesion requires the magnification of a microscope to be seen.